R/utils-internal.R

In terminological/ggrrr: Addressing Annoyances and Irritations

#' Get an optional function without triggering a CRAN warning
#'
#' You want to use a function if it is installed but don't want it to
#' be installed as part of your package and you don't want to reference it
#' as part of the Imports or Suggests fields in a package DESCRIPTION.
#'
#' @param pkg the package name
#' @param name the function you wish to use
#' @param alt a function that can be used instead
#'
#' @return the function you want if available or the alternative
#' @keywords internal
#' @export
#'
#' @examples
#' fn = .optional_fn("openssl", "md5", digest::digest)
#' as.character(fn(as.raw(c(1,2,3))))
.optional_fn = function(pkg, name, alt=function(...) {stop("function `",pkg,"::",name,"(...)` not available")}) {
  if (rlang::is_missing(name) || rlang::is_function(name) || rlang::is_formula(name)) {
    if (rlang::is_function(name) || rlang::is_formula(name)) alt = name
    tmp = unlist(stringr::str_split(pkg,stringr::fixed("::")))
    if (length(tmp) != 2) stop("either `name` must be supplied or the format `package::function` used for the `pkg` parameter")
    pkg = tmp[1]
    name = tmp[2]
  }
  alt = rlang::as_function(alt)
  if (!rlang::is_installed(pkg)) return(alt)
  return(utils::getFromNamespace(name, pkg))
}